1. Field of the Invention
The present invention relates to a positive chargeable color toner for developing electrostatic latent images in processes such as electrophotography, electrostatic recording and the like.
2. Relevant Art
Heretofore, nigrosine dyes are mainly being used as the charge control agent employed in positive chargeable toners for use in electrostatic load developing. However, although nigrosine dyes can be used in black colored toners because of their dark brown color, they are not appropriate for use in, for example, yellow, cyanogen, and magenta colored toners; as the charge control agent for use in color toners, colorless quaternary ammonium salt has been generally used. However, with this colorless quaternary ammonium salt there exist disadvantages such as poor dispersibility in regards to binder resin, and inferior charging properties when compared with nigrosine dyes.
As the binding resin for use in color toners, polyester resins, due to their superior light transparency and color stacking abilities, are preferably being employed. However, there exist problems in controlling charging properties since prior art charge control agents of quaternary ammonium salts and the like are affected by acid groups and hydroxy groups included in the aforementioned resins, resulting in unstable charging properties.
In addition, as the coloring agent for use in color toners, xanthene-type magenta colored dye, quinacridone-type magenta colored pigment, disazo-type yellow pigment, phthalocyanine-type cyanogen colored pigment and the like are known. These coloring agents are essential in color control of color toners, however, the charging properties vary according to the effects of their chemical structure, and thus these coloring agents do not always affect the positive chargeable toner in an ideal manner.
Furthermore, fluidity must also be among the characteristics of the toner, and in order to achieve this one or more types of fluidization agents are applied to the surface of the toner. Heretofore, as the fluidization agent for this toner, colloidal silica is being used. However, due to the strong intrinsic negative charging properties possessed by colloidal silica, when a positive chargeable toner employing colloidal silica is mixed inside a developing machine, there exist problems such as loss of the toner's original positive charging properties, fogging during developing, scattering of the toner, and accumulation of fluidization agent in the developer leading to reduction of the developer life span.